1. Field of the Invention
This invention relates to a method for the treatment of a surface of a shaped body formed of a synthetic organic polymer for the activation of the surface.
2. The Prior Art
Since synthetic organic polymers, such as polyolefins which consist only of saturated hydrocarbons and which are hydrophobic and highly crystalline in nature, generally has a low surface energy, the surfaces of shaped bodies such as sheets and fibers of such polymers are hard to be coated, printed, bonded or dyed. Therefore, it is necessary to pretreat such shaped bodies and to increase the surface energy thereof prior to coating, printing, bonding, dyeing or the like surface processing.
A variety of surface pretreating techniques have been hitherto proposed. For example, as pretreating methods for coating, printing and bonding, there are known a sand blast treatment, a treatment with vapor of a solvent, a treatment with a chromic acid mixture, a flame treatment, a corona discharge treatment, a plasma treatment, a functional groups-introducing treatment, a UV irradiation treatment, a treatment with phosphoric acid or naphthalenesulfonic acid, a satinizing treatment and a photo-grafting treatment. These conventional methods, however, are not entirely satisfactory for the reasons as set forth below.
The sand blast treatment method is one in which granules of a grinding material are caused to impinge on a surface of a shaped body to be treated for roughing same. The granular grinding material causes fouling of the working environment and the product. The surface of the treated product is, therefore, required to be washed with water. Further, there are caused problems that the treatment makes the surface opaque and that the grinding material once cut into the surface cannot be removed.
The solvent vapor treatment includes exposing, for a short period of time, a shaped body to vapors of a super-heated, halogenated hydrocarbon so that an amorphous portion of the surface of the shaped body is etched and swollen. It is, however, necessary to provide over the treated surface a primer layer containing chlorinated propylene prior to coating. In addition, unless the primer coat is provided immediately after the treatment, the treatment soon becomes ineffective. The treatment sometimes causes distortion of the shaped body. The treated surface should be heated for the removal of the solvent remaining after the coating. Additionally, this method is dangerous because of the necessity to handle vapors of a halogenated hydrocarbon which also tends to cause deterioration of the apparatus.
The treatment with chromic acid mixture includes heating the mixture (containing 75 parts of potassium bichromate, 120 parts of water and 1500 parts of concentrated sulfuric acid) to about 100.degree. C., and immersing a shaped body to be treated in the heated mixture for about 5 min. This method requires high costs for the treatment of the waste chromic acid mixture.
The flame treatment includes exposing the surface of a shaped body to be treated to an oxidizing flame (1000-2500.degree. C.) produced by the combustion of a gas containing an excess air. The surface is liable to be distorted or melted by the heat.
The corona discharge treatment includes passing a film or film-like body to be treated through a space between an electrode and a metal roller while applying a high electric voltage therebetween. This method is not applicable to other shaped bodies than those of a film-like form.
The plasma treatment includes exposing the surface of a plastic body to a low temperature plasma so that the surface undergoes a chemical change by the action of dissociated oxygen and ultraviolet rays. Plasma of oxygen or air is used. This method is disadvantageous because of the necessity of an expensive apparatus.
The functional groups-introducing method includes irradiating UV rays on the surface of a shaped body in an atmosphere of chlorine, and then treating the irradiated surface with an alkali. This method poses a problem of handling very dangerous chlorine gas.
The photo-grafting method includes admixing benzophenone with polypropylene powder, forming the admixture into a film, and photo-treating the surface of the film in the presence of acrylamide in an oxygen-free atmosphere for photochemically graft-copolymerizing the acrylamide with the polypropylene. This method requires complicated steps and is economically disadvantageous.
The UV irradiation treatment has a problem because the treatment requires a relatively long period of time in order to obtain desired results. Further, it is difficult to uniformly treat a surface of a shaped body to be treated.
The satinizing treatment includes immersing a polyacetal shaped body to be treated in a liquid bath containing p-toluenesulfonic acid, perchloroethylene-containing diatomaceous earth and dioxane at 80-120.degree. C. for 10-30 seconds. The treated body is then allowed to stand in air at 38-120.degree. C. for about 1 minute for drying and thereafter washed with water and dried. During this treatment perchloroethylene is vaporized to cause problems of bad odor and of variation of the composition of the bath.
The treatment with phosphoric acid or naphthalenesulfonic acid is effective only to specific polymers.
U.S. Pat. No. 4,853,253 issued to Katoh discloses a method in which a polymeric shaped body is first contacted with a UV-absorbing solvent at an elevated temperature and then the treated body is irradiated by UV rays with a wavelength of 1800-2100 .ANG.. While this method is effective to the activation of a flat surface, a shaped body with concaved portions into which a UV lamp is not able to be inserted cannot be activated satisfactorily.